Purification of fluids and in particular of water supplies is a long established field. For example it has been identified that water contaminated with, for example bacteria or viruses, can assist in the spread of water borne diseases. Additionally some substances, e.g. lead, are poisonous if consumed. Water can therefore be treated to remove harmful substances before it is consumed or used in order to assist in the prevention of disease.
There are a number of methods of removing unwanted or harmful substances from water. These include the performance of full- or part-sterilisation of the water to kill, denature or otherwise harm biological contaminants, for example bacteria. The addition of substances can also be performed to react with water-born chemical contaminants so as to transform these into removable or less harmful forms. Examples of approaches to sterilisation include the addition of chemicals such as chlorine or ozone, or the treatment of water with ultraviolet light. Examples of approaches to remove harmful substances by way of chemical reaction include the addition of water softeners, such as ion exchange resins, to remove chemicals such as ferrous iron, calcium and magnesium by ion exchange.
The use of ozone in water treatment is known to provide effective removal of unwanted substances in some applications. Ozone is a highly reactive molecule which readily reacts with a number of substances including biological substances such as viruses, bacteria, protozoa etc. Ozone treatment can also be expected to result in a lower risk of creating dangerous by-products than other methods such as the addition of chlorine. It has been established that a residual ozone concentration of 0.07 parts per million present for at least 1 second implies water fit for consumption. Thus in establishing a reliable ozone purification approach it may of utility to detect the concentration of ozone present in the water.
Existing methods of detecting the presence and concentration of ozone in water include chemical titration, separation of ozone from water using a membrane then reacting this with a catalyst and using electrochemistry to monitor the products, and monitoring the absorption of UV light by ozone in water.
The first two of these methods require that the water be removed from a system and tested before the ozone concentration can be detected. Detection of the concentration of ozone is therefore delayed until the relevant tests and reactions have been carried out, during which time the water may need to be stored before it is confirmed that it is safe to distribute.
Additionally, these methods may require frequent sampling and associated testing, which may require a high degree of human input for all of the accessing water for sampling, sampling and testing.
Monitoring the absorption of UV light is used in large industrial ozone plants. Very few other gases absorb light as strongly as ozone in the deep UV frequencies and thus the use of UV light can provide a reliable ozone detection method. This method can also provide results rapidly, for example without having to wait for results of chemical reactions. However UV based ozone detectors are typically very large and very expensive. UV based ozone detectors typically have low portability due to the use of UV discharge lamps that require careful handling. Such discharge lamps may also have a limited life span and therefore require regular replacement, bringing therewith associated cost and human input.
Known approaches for measuring the concentration of a substance in a fluid are described in US2003025909A, US2008304048A, JP2001056292A, JP2002005826A, JP200306592A, JP2003329585A, JP2011169875A, JP3131741A, JP3223726B, RU143323U and RU44181U.